The present invention relates to a structure for sealing the gap between two concentric machine parts which are arranged to move, in particular to rotate, relative to each other, the outer machine part being provided with a groove while the inner one comprises a plain contact surface arranged opposite the said groove, the sealing ring structure comprising a sealing ring made of a tough-elastic plastic material and fitted into the groove and being provided with a sealing edge bearing against the contact surface of the inner machine part, and a stressing ring made of a rubber-elastic material, which stressing ring surrounds the sealing ring, loads it radially at its outer surface and generates a pressure maximum at the sealing edge.
Sealing ring structures of this type have been known in many different forms. It is common to all of them that the stressing ring serves the function not only to influence the contact pressure prevailing at the sealing edge of the sealing ring, but also to seal the sealing ring relative to the groove in the outer machine part. The rubber-elastic stressing ring is sized for this purpose in such a manner that it is fixed in place between the cylindrical outer surface and the base of the groove which is arranged concentrically therewith.
It is a frequently encountered problem with these sealing structures that the sealing ring may get displaced, i.e. may rotate relative to the stressing ring. For example, an expansion due to temperature differences may cause the sealing ring to stick to the plain contact surface of the inner machine part, which situation may lead to a sliding movement between the sealing ring and the elastomeric stressing ring. However, such a condition leads very rapidly to overheating of the sliding surface between the two rings and, consequently, to failure of the seal because the frictional heat cannot be carried off with sufficient rapidity through the plastic material of the rings.
A sealing ring structure known from DE-OS No. 32 07 327 tries to prevent the two rings of the sealing ring structure from rotating relative to each other by the use of radial pins which are fixed in the outer stressing ring and engage radial bores in the inner sealing ring. It has been found, however, that the radial pins are not sufficient to absorb the forces generated by relative movements between the two rings but that, quite to the contrary, when the operating conditions give rise to relative movements between the two rings, the rings will be destroyed by the pins engaging them.